1. Field of the Invention
The present invention relates to a flow control valve used in parts, for which carrying out flow control is required, such as breather circuits for fuel tanks.
2. Description of the Related Art
In the vicinity of automobile fuel tanks, a vaporized-fuel circulating system, a so-called evaporator circuit, is disposed. The evaporator circuit leads vaporized fuels from fuel tanks to external canisters. The vaporized fuels are then adsorbed to activated carbon, and are stored temporarily therein. Thus, the evaporator circuit inhibits the pressure increment within fuel tanks, and at the same time prevents the vaporized fuels from being emitted into the outside air. The canisters are connected with engines, and engines exert an inlet negative pressure to release the adsorbed vaporized fuels from activated carbon to remix them into an air-fuel mixture. Accordingly, the adsorbed vaporized fuels are reused as fuels.
However, when a fuel sucks in fresh air through a fuel supply opening in a large volume in supplying fuel to an automotive fuel tank, fuel vaporizes facilitatively in the fuel tank. Accordingly, the volume of gases flowing to the canister increases. Consequently, the adsorption amount of gases to the canister has increased. Thus, it is needed to enlarge the canister. However, an enlarged canister causes a problem in view of designing for balancing the size and the installation space. Hence, the fuel tank is provided with a breather tube which communicates the gaseous phase in the fuel tank with the outside air. The breather tube is connected with an inlet pipe adjacent to a fuel supply opening of the inlet pipe at one of the opposite ends. Moreover, a breather nipple, which is fixed so as to communicate with the gaseous phase in the fuel tank, is fitted into the other opposite end of the breather tube. Therefore, the vaporized fuel present within the fuel tank in supplying fuel passes the breather tube through the breather nipple, and circulates again to the fuel tank by way of the inlet pipe. Thus, the fuel is inhibited from sucking in fresh air. In addition, it is possible to reduce the adsorption amount of vaporized fuel to the canister, because the fuel is inhibited from vaporizing.
Note that an orifice for controlling a breather gas volume is usually formed in the breather nipple so as not to increase the breather gas volume, which circulates from the breather tube to the inlet pipe, more than an air volume, which is sucked in at the fuel supply opening. Hereinafter, the circuit of gas circulating from the fuel tank, the breather nipple, the breather tube, the inlet pipe, and again to the fuel tank in this order will be referred to as a breather circuit.
Here, the fuel-supply rate in supplying fuel to fuel tanks can be divided into two types, a low rate represented by 15 L/min. and a fast rate represented by 38 L/min., depending on the specification and usage of fuel supply guns. Moreover, it is required to increase the breather gas volume circulating in the breather circuit in fast-rate fuel supply, because fuels suck in air more in the first-rate fuel than in the low-rate fuel supply.
In order to increase the breather gas volume circulating the breather circuit in fast-rate fuel supply, it is effective to enlarge the opening of the orifice. However, when enlarging the opening of the orifice, the breather gas volume circulating the breather circuit has increased even in low-rate fuel supply. Accordingly, the breather gas volume circulating the breather circuit has surpassed the sucked-in air volume in a low-rate fuel-supply range. Consequently, vapor leakage might occur through the fuel supply opening.
On the contrary, when diminishing the opening of the orifice, it is possible to prohibit vapor leakage in low-rate fuel supply. However, the volume difference has increased between the sucked-in air volume and the breather gas volume in fast-rate fuel supply. Accordingly, sucked-in fresh air facilitates the vaporization of fuel in the fuel tank. Consequently, the adsorption amount of vaporized fuel to the canister has enlarged.
FIG. 6 shows a conceptual diagram for illustrating the above-described relationships. In actuality, fuel supply is carried out at two levels, low-rate fuel supply and fast-rate fuel supply, however, FIG. 6 shows that the fuel-supply rate increases or decreases continuously. As indicated with the line “A,” the sucked-in air volume depends on the fuel-supply rate continuously. As indicated with the curve “B,” in a minor-opening-diameter orifice simulating low-rate fuel supply, the breather gas volume increases parallel to the sucked-in air volume in low-rate fuel supply, but the volume difference has enlarged between the sucked-in air volume and the breather gas volume as the fuel-supply rate increases. Accordingly, the sucked-in fresh air facilitates the vaporization of fuel in the fuel tank. Consequently, the adsorption amount of vaporized fuel to canister has enlarged. On the other hand, as indicated with the curve “C,” in a major-opening-diameter orifice simulating fast-rate fuel supply, the breather gas volume surpasses the sucked-in air volume in a low-rate fuel-supply range. As a result, vapor leakage occurs.
That is, it is difficult for conventional breather nipples provided with a single orifice to cope with the required increment/decrement of breather gas depending on the increment/decrement of fuel-supply rate.
Hence, Japanese Unexamined Patent Publication (KOKAI) No. 8-216,707 proposes an apparatus for prohibiting evaporating fuel gases from being emitted, apparatus which is provided with variable means for controlling the circulation volume of evaporating fuel gases. Moreover, Japanese Unexamined Patent Publication (KOKAI) No. 2003-28,010 proposes to dispose a connector equipped with a built-in valve in a breather circuit, valve which controls the circulation volume of evaporating fuel gases depending on a pressure.
In the techniques disclosed in the patent publications, however, a valve for opening/closing a fluid passage is simply disposed in a breather circuit. Therefore, it is difficult to adequately control the breather gas volume in both low-rate fuel supply and fast-rate fuel supply. The disadvantage will be hereinafter described with reference to FIG. 7.
The breather gas pressure is affected greatly by temperature as well. Accordingly, the breather gas pressure fluctuates in low-rate fuel supply and fast-rate fuel supply, respectively. Consequently, when the breather gas volume to be secured in low-rate fuel supply is designated at “α” in FIG. 6 and the breather gas volume to be secured in fast-rate fuel supply is designated at “β” in the drawing, the relationship between ideal breather gas pressure and breather gas volume appears to be a curve “D” in the drawing. The breather gas pressure varies in a width of from “a” to “b” in the drawing in low-rate fuel supply, and varies in a width of from “c” to “d” in the drawing in fast-rate fuel supply.
However, the conventional techniques only employ such a structure that a valve opens as the breather gas pressure increases to gradually enlarge the breather gas volume. Accordingly, when the valve is adjusted to open at the maximum breather gas pressure designated at “b,” for example, which is assumed to be a pressure for not causing vapor leakage through the fuel supply opening in low-rate fuel supply, the relationship between the breather gas pressure and the breather gas volume appears to be a curve “E” in the drawing. Consequently, when the breather gas pressure fluctuates in a lower range in fast-rate fuel supply as designated at a point “X” in the drawing, the breather gas volume comes short so that the volume of gas, which flows to the canister, has enlarged.
On the other hand, when the valve is adjusted to open at the minimum breather gas pressure designated at “c,” which is assumed to be a pressure for substantially securing a predetermined breather gas volume in fast-rate fuel supply, the relationship between the breather gas pressure and the breather gas volume appears to be a curve “F” in the drawing. Consequently, when the breather gas pressure fluctuates in a higher range in low-rate fuel supply as designated at a point “Y” in the drawing, the breather gas volume becomes excessive so that vapor leakage has occurred.
Moreover, in the conventional techniques, the variable means for controlling the circulation volume of evaporating fuel gases depending on their pressure is disposed midway in the breather circuit. Accordingly, the conventional techniques suffer from not only the problem of the increased number of component parts but also the problem of the installation space. In addition, the variable means further causes a ventilation resistance in the breather circuit. Consequently, there arises a problem that the control for the conventional apparatus or connector becomes so unstable that it is less likely to control the breather gas volume, compared with the case where the breather gas volume is controlled by the inner pressure of fuel tank itself.
Incidentally, it has been required for breather tubes to provide reduced installation space. Hence, a breather tube is usually disposed in the following manner: a breather tube is disposed along an inlet pipe as much as possible; is bent thereafter at the leading end substantially perpendicularly; and is connected with a branched pipe which protrudes from a peripheral wall of the inlet pipe. Moreover, the substantially-perpendicularly-bent part of the breather tube and the branched pipe of the inlet pipe can desirably have short lengths as much as possible, respectively. However, in the connector equipped with the built-in valve disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 2003-28,010, not only a gas flow passage is formed linearly, but also it is equipped with the built-in valve. Accordingly, the connector has a long overall length relatively. Consequently, when the connector equipped with the built-in valve disclosed in the patent publication is disposed in a breather circuit, a breather tube has produced an enlarged installation space if the connector is disposed so as to be connected with a branched pipe which protrudes from a peripheral wall of the inlet pipe. As a result, it is inevitable to dispose the leading end of the breather tube along the inlet pipe. In this instance, however, it is required to bend the branched pipe, which protrudes from a peripheral wall of the inlet pipe and which is connected with the connector, in a letter “L” shape to result in a drawback in view of manufacturing cost. In short, the connector equipped with the built-in valve disclosed in the patent publication suffers from the drawbacks of limited installation disposition and low degree of designing freedom.
Moreover, when assembling the connector equipped with the built-in valve disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 2003-28,010, paired linear component parts are first prepared. Then, fine component parts, such as a valve and a spring, are accommodated in one of the paired linear component parts. Finally, it is required to connect the other one of the paired component parts with the one of the paired linear component parts, in which the fine component parts are accommodated, so as to house the one of the paired linear component parts therein. Thus, the connector disclosed in the patent publication comprises a large number of component parts in assembly, and accordingly has a problem of poor manufacturing operability.